Vacuum may be used as a device actuating medium in a vehicle. For example, vacuum may be used to assist a driver applying vehicle brakes. In particular, vacuum operates on a brake booster diaphragm to increase an amount of force applied to vehicle brakes when a driver depresses a brake pedal. However, if the vehicle includes a smaller displacement engine, it may be difficult for the engine to provide as much vacuum as is desired via its intake manifold or an ejector. One way of improving an amount of vacuum generated by an engine is to reduce engine load so that less air is necessary to keep the engine running. However, it may not always be possible to reduce engine load when additional vacuum is desired. Further, even if some loads can be shed from the engine so that the engine may provide additional vacuum, shedding the loads may reduce engine efficiency, vehicle drivability, and/or driver comfort.
The inventor herein has recognized the above-mentioned issues and have developed an engine method, comprising: during a first condition, reducing a first engine operating parameter and a second operating parameter in an alternating manner in response to a desired engine intake manifold vacuum; and during a second condition, reducing the first engine operating parameter followed by reducing the second engine operating parameter.
By adjusting an engine speed and load applied to an engine by an alternator or another engine speed dependent device in an alternating manner, it may be possible to improve vacuum generation via the engine. Further, engine output torque may be maintained at a level that provides improve vehicle drivability and driver comfort while vacuum is being produced by the engine. For example, load of a device coupled to the engine, such as an alternator, may be incrementally reduced to lower engine load. Between each incremental reduction in load applied to the engine, the engine speed may be adjusted to further reduce load provided to the engine by engine speed dependent devices. The adjustments to load applied to the engine and engine speed may be stopped when engine intake manifold vacuum reaches a threshold vacuum so that extra vacuum is not provided and so that the engine operates more efficiently. Further, the engine may continue to supply power to the load device to improve vehicle drivability and driver comfort while vacuum generation by the engine is increasing. In this way, engine efficiency may be improved while a desired amount of vacuum is provided by the engine.
The present description may provide several advantages. In particular, the approach may improve engine efficiency when the engine is providing vacuum. Further, the approach may account for different devices that have opposite engine speed dependent effects on load applied to the engine. Further still, the approach may improve vehicle drivability by allowing partial performance of some engine loads.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.